The incidence rates of common forms of kidney disease including that attributed to hypertension are significantly higher in African Americans, relative to Caucasians. Racial differences in the frequency of Apolipoprotein L1 gene (APOL1) variants are now known to account for these differences. APOL1 risk variants rose to high frequency in African Americans since one copy protects from the parasite that causes African sleeping sickness, a potentially fatal disease. Approximately 10% of African Americans inherit two copies of APOL1 risk variants, placing them at a ten-fold increased risk for kidney disease. The mechanism whereby APOL1 gene variants contribute to kidney disease is unknown. This application proposes to determine how APOL1 gene variants contribute to kidney disease, information likely to yield more effective therapies. Existing therapies including strict blood pressure control have had disappointing results. We propose to determine whether: (1) variation in the APOL1 gene in kidney cells directly leads to cell dysfunction with resultant kidney disease, and/or (2) abnormal circulating ApoL1 proteins (high density lipoprotein [HDL] bound or lipid-free) lead to kidney disease. To explore mechanism 1, gene expression profiles will be examined in kidney cells from African Americans with and without APOL1 risk variants to determine which genes and gene pathways are over expressed (turned up) or under expressed (turned down), based upon the APOL1- specific genetic make-up of the cells. To explore mechanism 2, the amount and binding patterns of circulating ApoL1 proteins to HDL will be examined based upon an individual's genetic make- up. Kidney cells will be exposed to normal and risk ApoL1 proteins in vitro to determine whether risk variant proteins are toxic to cells and how this toxicity manifests. Based on these studies, additional analyses may be conducted in transgenic mice expressing normal and variant APOL1 to assess renal effects and in vivo metabolism of ApoL1 proteins. We will also attempt to identify undetected kidney disease risk variants in the APOL1 gene by deeply sequencing the surrounding chromosomal region. These experiments are likely to determine the mechanisms whereby APOL1 gene variants lead to non-diabetic kidney disease and assist in finding a cure for this devastating disease disproportionately impacting the African American community.